Population Variation of Complex Advertisement Calls in Physalaemus petersi and Comparative Laryngeal Morphology
Populations of Physalaemus petersi show extraordinary variation in the expression of facultative complex calls. Previous studies have shown that a structure in the larynx, the fibrous mass (FM1), is correlated with variation in production of the complex call among taxa in the Physalaemus pustulosus species group. We tested the hypothesis that the variation in the presence of call complexity that occurs within P. petersi mirrors the same laryngeal variation associated with complex calls among other species of the genus. We examined calls and larynges of P. petersi from populations on a north-south transect on the western side of its Amazonian distribution. All four populations of P. petersi (Peru and Brazil) in the south produce complex calls, whereas only one population of five in the north (Ecuador) produce complex calls. We compared larynges of four populations of P. petersi, two that produce complex calls and two that do not. We then compared them to larynges of P. pustulosus, which produces complex calls, and to Physalaemus coloradorum, which does not produce complex calls. The FM1 is significantly larger in populations of P. petersi that produce complex calls than those without complex calls. FM1 sizes of populations of P. petersi were more similar to other species with the same call type than they were to populations of their own species with a different call type. These data suggest several interpretations of the evolution of complex calls and the associated underlying morphology.Abstract
Images of anuran larynges. (A) Drawing of an anuran hyolaryngeal structure, taken from Duellman and Trueb (1986). AC = arytenoid cartilage, CrC = cricoid cartilage, BP = bronchial process. To the right is a cross-sectional view of the anuran larynx, adapted from Martin (1972) and Duellman and Trueb (1986). The vocal folds, VF, and a fibrous mass, FM, can be seen in this view. (B) Cross-sectional view of a larynx of Physalaemus pustulosus, from Ryan and Drewes (1990). The primary fibrous mass, FM1, occludes the airway. A transverse thickening, TS, of the vocal folds is also shown here. (C) Drawing of the ventral or cardiac view of a Physalaemus petersi larynx without the musculature and hyoid plate, showing the opposite side of the larynx to (A), with the AC hidden from view. The BP is at the entrance to the lungs and the FM1 occludes the airway. The CrC is removed on the right side of the larynx, exposing the FM1 embedded in the vocal folds, VF. The smaller FM2 is positioned anterior to the FM1. (D) Photographs of a Yasuní male's larynx. From left to right: ventral, side, and posterior view. The dotted lines represent the measured FM1 and BP areas
Map of northwestern South America with locations of Physalaemus petersi populations. The two shaded areas represent the northern and southern regions, enlarged on the right. From north to south: L = La Selva, Y = Yasuní, J = Jatun Sacha, C = Cando, B = Boca do Tejo, R = Restauraçao, X = Xapuri, T = Tambopata
Oscillograms and sonograms of Physalaemus petersi, Physalaemus pustulosus, and Physalaemus coloradorum. All calls are uniformly scaled. (A) Representatives of simple calls from populations of P. petersi and P. coloradorum. L = La Selva, C = Cando. (B) Representatives of complex calls from populations of P. petersi and P. pustulosus. Y = Yasuní, T = Tambopata
Mean and standard error plots of measurements for each population. Populations of Physalaemus petersi with complex calls are on the left side of the line and the populations with simple calls are on the right side on the X–axis. On the far right is a species with simple calls, Physalaemus coloradorum and on the left is Physalaemus pustulosus, a species with complex calls. (A) Measurements of the fibrous mass size summed in three views, adjusted for SVL body size. (B) Measurements of larynx size, adjusted for body size. (C) Measurements of the fibrous mass area summed in three views, adjusted for larynx area. (D) Measurement results of the bronchial process (BP) area from the posterior view, adjusted for larynx area
Contributor Notes
Section of Integrative Biology C0930, University of Texas, Austin, Texas 78712. (KEB) kathyboul@mac.com; and (MJR) mryan@mail.utexas.edu Send reprint requests to MJR.